Core composition for casting, and method for preparing core for casting using the same

ABSTRACT

Disclosed are a core composition for casting and a method for preparing a core for casting using the composition. The core composition for casting includes: molding sand; a binder that includes a water glass-based binder and an oxide film inhibitor; and an additive, thereby improving a sand removing property without releasing harmful gases.

TECHNICAL FIELD

The present invention relates to a core for casting that may improve a sand removing property without releasing harmful gases. Further, the present invention relates to a method for preparing a core for casting using the composition.

BACKGROUND

Generally, when a casting having a hole such as a cylinder is made by a casting work, a mold having a shape corresponding to the hole is referred to as a core. In other words, when performing a casting process of a casting having a hole or a hollow casting, a molten casting material is injected into a mold after a core is placed inside the mold, and when the casting is hardened, the casting and the core are removed from the mold, and then the core is removed from the casting.

Meanwhile, as a method for preparing the core, molding sand and a shape binder are introduced to a mold, and the shape binder is cured and formed to a prescribed shape. The molding sand may be common sand, and an organic binder is typically used as the shape binder. The organic hinder has advantages such as a fast curing rate, however, harmful influences may occur in casting environment, for example, the life span of a casting mold may be reduced by the harmful gases, and condensates and the like may occur during casting.

In view of the above, researches for using an inorganic binder instead of an organic binder have been progressed. For example, use of water glass-based binder have been introduced. When a core is prepared using a water glass-based binder, harmful effects by the use of organic binders may be reduced. However, when the water glass-based binder is used, flexure strength is reduced compared to organic binders, and the strength is rapidly reduced due to a weakening bonding power caused by a hygroscopic property of water glass depending on the time left unattended.

In addition, the water glass-based binder may be vitrified at a high temperature of about 540° C. or greater, and when sand is removed after casting using the water glass-based binder, the molding sand may adhere to the surface of a casting product such that post treatments may be complicated.

The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.

SUMMARY OF THE INVENTION

In a preferred aspect, the present invention provides a core composition for casting. The core composition may include a water glass-based binder together with an additive for sand removal such as zinc oxide, thereby substantially reducing flexure strength at high temperatures, such that the core composition may improve a sand removing property. In a further preferred aspect, the present invention provides a method for preparing a core for casting using the core composition.

In an exemplary embodiment, core composition the casting may include: molding sand; a binder; and an additive. In particular, the binder may include water glass-based binder and an oxide film inhibitor. The additive may be added for sand removal.

The oxide film inhibitor may include sodium hexametaphosphate, sodium pyrophosphate or a combination thereof, and the oxide film inhibitor may be included in amount of about 0.1 to 0.3% by weight with respect to the total weight of the core composition.

In addition, the additive for sand removal may be include zinc oxide powder and may be included in an amount of about 0.4 to 0.6% by weight with respect to the total weight of the core composition.

The binder for a core may be included in an amount of about 4 to 6 parts by weight with respect to 100 parts by weight of the molding sand. In particular, the water glass-based binder may be formed with about 8 to 10 parts by weight of Na₂O and about 25 to 30 parts by weight of SiO₂ with respect to 100 parts by weight of the binder for a core, and the molar ratio of the SiO₂:Na₂O may range from about 10 to about 3.3.

The invention also provides the above composition that consists essentially of, or consist of the components. For example, a core composition may consist essentially of, or consist of: mold sand; a binder in amount of about 4 to 6 parts by weight with respect to 100 parts by weight of the molding sand, where the binder consists essentially of an amount of about 8 to 10 parts by weight of Na₂O and about 25 to 30 parts by weight of SiO₂ with respect to 100 parts by weight of the binder and a oxide film in amount of about 0.1 to 0.3% by weight with respect to the total weight of the core composition; and a zinc oxide powder in an amount of about 0.4 to 0.6% by weight with respect to the total weight of the core composition.

In an exemplary embodiment, a method for preparing a core for casting using the core composition for may include: preparing a mixture of components of a core composition; supplying the mixture to a core mold; and dehydrating a binder by supplying heat and hot air to the core mold supplied with the mixture to form a core for casting.

In particular, the heat may be applied a temperature range of about 150 to 180° C., and the hot air may be supplied at a temperature range of about 170 to 190° C.

Further provided are casting products that are manufactured using the core composition as described above. Still further provided are vehicles comprising a casting product that is manufactured using the core composition as described above

According to various exemplary embodiments of the present invention, rapid reduction of flexure strength may be prevented even when the core is left unattended in the atmosphere. In addition, after the core is exposed at high temperatures, flexure strength may be reduced thereby improving a sand removing property, and consequently, costs for post treating the adhesion of molding sand may be reduced. Moreover, by using an inorganic binder rather than an organic binder, the release of harmful gases may be prevented when casting, and thus, environmentally friendly casting may be provided.

Other aspects of the invention are disclosed infra.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph comparing flexure strength depending on the presence of an oxide film inhibitor;

FIG. 2 is a graph comparing flexure strength depending on the types of a binder added to a composition for casting;

FIG. 3 shows a photograph of the surface of a conventional aluminum casting product casted using a conventional core for casting that does not include an exemplary additive according to an exemplary embodiment of the present invention for sand removal;

FIG. 4 shows a photograph of the surface of an exemplary aluminum casting product casted according to an exemplary embodiment of the present invention, using a core for casting that includes zinc oxide powder in an amount of about 0.5% by weight with respect to the total weight of the core composition;

FIG. 5 shows a photograph of a core for casting prepared without supplying hot air to a mold; and

FIG. 6 shows a photograph of an exemplary core for casting prepared by supplying hot air corresponding to a temperature range of about 170 to 190° C. to a mold according to an exemplary embodiment of the present invention.

Reference numerals set forth in the FIGS. 1-6 include reference to the following elements as further discussed below:

100: A core for casting prepared as one example of the present invention using a core composition for casting according to the present invention containing an oxide film inhibitor in 0.2% by weight.

200: An existing core for casting prepared using a core composition for casting that does not contain an oxide film inhibitor

300: Molding Sand

400: Aluminum Casting Product

DETAILED DESCRIPTION

It is understood that the term “vehicle” or “vehicular” or other similar term as used herein is inclusive of motor vehicles in general such as passenger automobiles including sports utility vehicles (SUV), buses, trucks, various commercial vehicles, watercraft including a variety of boats and ships, aircraft, and the like, and includes hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles and other alternative fuel vehicles (e.g. fuels derived from resources other than petroleum). As referred to herein, a hybrid vehicle is a vehicle that has two or more sources of power, for example both gasoline-powered and electric-powered vehicles.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

Unless specifically stated or obvious from context, as used herein, the term “about” is understood as within a range of normal tolerance in the art, for example within 2 standard deviations of the mean. “About” can be understood as within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the stated value. Unless otherwise clear from the context, all numerical values provided herein are modified by the term “about”.

Hereinafter, the present invention will be described in detail with reference to attached drawings.

The present invention provides a core composition for casting which may include: molding sand; a binder for a core; and an additive. Particularly, the binder may include a water glass-based binder and an oxide film inhibitor. The additive may be used for sand removal.

The molding sand, as used herein, may generally include any sand used for the production of a casting. I particular, particle sizes of the molding sand may range from about AFS GFN (America Foundry Society Grain Fineness Number) 30 to 50.

The binder for a core may be a material used for favorable tangling by applying viscosity, and may include a water glass-based binder and an oxide film inhibitor. The binder for a core may be included in an amount of about 4 to 6 parts by weight with respect to 100 parts by weight of the molding sand.

Particularly, to obtain optimal flexure strength, the water glass-based binder may be formed with an amount of about 8 to 10 parts by weight of Na₂O and an amount of about 25 to 30 parts by weight of SiO₂ in with respect to 100 parts by weight of the binder for a core, and the molar ratio of the SiO₂:Na₂O may ranges from about 1:3.0 to 1:3.3.

The oxide film inhibitor, as used herein, may prevent the loss of binding power due to a reversible reaction caused by a hygroscopic property form the water glass-based binder substantially, and the rapid reduction of flexure strength may be eliminated by increasing the pot life of the water glass-based binder.

Particularly, the oxide film inhibitor may include sodium hexametaphosphate, sodium pyrophosphate or a combination thereof, and the oxide film inhibitor may be included in an amount of about 0.1 to 0.3% by weight with respect to the total weight of the core composition to prevent the rapid reduction of flexure strength.

The additive for sand removal, as used herein, may improve a sand removing property such that the sand in the casted core may be readily removed, and particularly, the additive for sand removal may include zinc oxide powder. The zinc oxide powder may included in an amount of about 0.4 to 0.6% by weight with respect to the total weight of the core composition. When be additive for sand removal is included in less than about 0.4% by weight, the effects of improving the sand removing property may not be sufficient, and when the additive for sand removal is included in greater than about 0.6% by weight, mixing may not be sufficiently performed due to sand condensation.

The present invention also provides a method for preparing a core for casting.

Particularly, a mixture may be prepared by mixing components of the core composition for casting as described above. The core composition for casting may include: molding sand; a binder for a core including a water glass-based binder and an oxide film inhibitor; and an additive for sand removal. Further, the composition for the method may include other core components of the core composition for casting as described above.

Particularly, flexure strength which may be reduced due to a hygroscopic property of the water glass-based binder may be prevented by the oxide film inhibitor and by adding the additive for sand removal, such that the sand in the prepared core may be readily removed from a casting product later.

Subsequently, the prepare mixture may be supplied to a core mold, and then a core for casting may be prepared as a binder for a core is dehydrated. The binder may be dehydrated efficiently by supplying heat and hot air to the core mold supplied with the mixture and the like. The heat may be applied at a temperature range of about 150 to 180° C., and the hot air may be supplied at a temperature range of about 170 to 190°;

EXAMPLE

Hereinafter, the present invention will be described in more detail with reference to examples. However, these examples are for illustrative purposes only, and it will be obvious to those skilled in the art that the scope of the present invention is not interpreted to be limited to these examples.

FIG. 1 is a graph comparing flexure strength depending on the presence of an oxide film inhibitor.

As shown in FIG. 1, when a conventional core for casting prepared uses a convention core composition that does not contain an oxide film inhibitor (200), the flexure strength was rapidly reduced as the time of the core being left unattended in the atmosphere passed. However, a core for casting prepared using a core composition containing an oxide film inhibitor in an amount of about 0.2% by weight (100) according to an exemplary embodiment of the present invention maintained flexure strength of about 60 kw/cm² or greater even after about 96 hours.

FIG. 2 shows a graph comparing flexure strength depending on the types of a binder added to a core composition the casting.

As shown in FIG. 2, the flexure strength of a core for casting prepared according to an exemplary embodiment of the present invention using a core composition for casting including a binder was about 60kg/cm² or greater, which was significantly improved compared to the flexure strength of the conventional core for casting using only a water glass-based binder. This flexure strength was about equal to the flexure strength of a conventional core for casting prepared using an organic binder may be obtained.

FIG. 3 shows a photograph of the surface of a conventional aluminum casting product casted using a core for casting that does not include an additive for sand removal, and FIG. 4 shows a photograph of the surface of an exemplary aluminum casting product casted using an exemplary core for casting that includes zinc oxide powder in an amount of about 0.5% by weight with respect to the total weight of the core composition.

When casting was carried out using a core for casting that does not include an additive for sand removal, large amounts of molding sand (300) adhered to the surface of a aluminum casting product (400). However, when casting was carried out using an exemplary core for casting that includes zinc oxide powder, the sand removing property was greatly improved and the adhesion of molding sand (300) barely occurred.

FIG. 5 shows a photograph of a core for casting prepared without supplying hot air to a mold, and FIG. 6 shows a photograph showing an exemplary core for casting prepared by supplying hot air corresponding to a temperature range of about 170 to 190° C. to a mold. The core for casting may be obtained from dehydrating the binder for a core by supplying hot air to a mold.

Although the exemplary embodiments of the present invention have been described, it should be noted that the spirit of be present invention is not limited to the exemplary embodiments set forth herein and those skilled in the art and understanding the present invention can easily accomplish other exemplary embodiments included in the spirit of the present invention by the addition, modification, and removal of components within the same spirit, but those are construed as being included in the spirit of the present invention.

While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. 

1. A core composition for casting, comprising: molding sand; a binder that includes a water glass-based binder and an oxide inhibitor; and an additive.
 2. The core composition of claim 1, wherein the oxide film inhibitor includes sodium hexametaphosphate, sodium pyrophosphate, or a combination thereof.
 3. The core composition of claim 2, wherein the oxide film inhibitor is included in an amount of about 0.1 to 0.3% by weight with respect to the total weight of the core composition.
 4. The core composition of claim 1, wherein the additive for sand removal is formed with zinc oxide powder,
 5. The core composition of claim 4, wherein the additive for sand removal is included in an amount of about 0.4 to 0.6% by weight with respect to the total weight of the core composition.
 6. The core composition of claim 1, wherein the binder is included in an amount of about 4 to 6 parts by weight with respect to 100 parts by weight of the molding sand
 7. The core composition of claim 6, wherein the water glass-based binder includes an amount of about 8 to 10 parts by weight of Na₂O and an amount of about 25 to 30 parts by weight of SiO₂ with respect to 100 parts by weight of the binder for a core.
 8. The core composition of claim 7, wherein a molar ratio of the SiO₂:Na₂O ranges from about 1:3.0 to about 1:3.3.
 9. A core composition for casting, consisting essentially of: mold sand; a binder in amount of about 4 to 6 parts by weight with respect to 100 parts by weight of the molding sand, the binder consisting essentially of an amount of about 8 to 10 parts by weight of Na₂O and about 25 to 30 parts by weight of SiO₂ with respect to 100 parts by weight of the binder and a oxide film in amount of about 0.1 to 0.3% by weight with respect to the total weight of the core composition; and a zinc oxide powder in an amount of about 0.4 to 0.6% by weight with respect to the total weight of the core composition.
 10. A method for preparing a core for casting, comprising: preparing a mixture by mixing components of a core composition for casting, the composition comprises: molding sand, a binder that includes a water glass-based binder and an oxide film inhibitor and an additive; supplying the mixture to a core mold; and dehydrating the binder by supplying heat and hot air to the core mold supplied with the mixture.
 11. The method of claim 10, wherein the heat is applied at a temperature range of about 150 to 180° C., and the hot air is supplied at a temperature range of about 170 to 190° C.
 12. The method of claim 10, wherein the oxide film inhibitor includes sodium hexametaphosphate, sodium pyrophosphate, or a combination thereof.
 13. The method of claim 12, wherein the oxide film inhibitor is included in an amount of about 0.1 to 0.3% by weight with respect to the total weight of the core composition.
 14. The method of claim 10, wherein the additive for sand removal is formed with zinc oxide powder.
 15. The method of claim 14, wherein the additive for sand removal is included in an amount of about 0.4 to 0.6% by weight with respect to the total weight of the core composition.
 16. The method of claim 10, wherein the binder is included in an amount of about 4 to 6 parts by weight with respect to 100 parts by weight of the molding sand.
 17. The method of claim 10, wherein the water glass-based binder includes an amount of about 8 to 10 parts by weight of Na₂O and an amount of about 25 to 30 parts by weight of SiO₂ with respect to 100 parts by weight of the binder for a core.
 18. The method of claim 17, wherein a molar ratio of the SiO₂:Na₂O ranges from about 1:3.0 to 1:3.3.
 19. A casting product obtained using a core composition of claim
 1. 20. A casting product obtained from a method of claim
 10. 